This invention relates to a novel compound bearing an urethane linkage useful as a plasticizer for polyvinyl chloride (PVC) and a process for preparing the compound. This compound is an adduct of ricinoleic esters and an isocyanate, which is prepared by the process of the present invention is new and has formula 1 of the drawings enclosed with the specification.
The invention specifically relates to a process for the preparation of a compound bearing an urethane linkage useful as a plasticizer for poly vinylcllloride (PVC). The compound prepared by the process of the present invention is new and has the formula 1 shown in the drawings accompanying this specification. The compound of formula 1, is derived from a fatty acid ester bearing a hydroxyl functionality and/or compound containing isocyanate functionality. More specifically, the invention relates to a process for the preparation of urethane type compound of formula 1 of the drawings annexed with the specification having molecular weight in the range of 650 to 900.
The compound of formula 1, prepared by the process of the present invention has excellent compatibility with PVC on account of the desirable functional groups present in the molecule. Hence, the invention further provides a process for the preparation of improved compounded PVC employing the urethane type compound of formula 1 of the drawings enclosed with the specification.
It is well known in the prior art that addition of organic compounds, called plasticizers, to PVC confers on the PVC desirable properties such as flexibility, softness, good feel and ease of processability, extensibility and lower melting temperature [Encyclopedia of PVC Vol. 1 and 2, L. I. Nass (1976)]. Plasticizers function by dissolving in PVC, reducing the cohesive energy density between the polymer chains and reducing the polar forces exerted by the halogen atoms present in PVC. For any organic compound to function as an effective plasticizer for PVC it must possess (a) very high miscibility with PVC, (b) must have polar groups and (c) must have a low tendency to diffuse and migrate out of the polymer during its effective service life. In addition, the plasticizer must not cause colouration to PVC, should be non toxic, odorless, possess low volatility and thermally stable at the temperature of mixing and compounding PVC with plasticizer.
A variety of organic compounds have been reported as effective plasticizers for PVC. These include esters of phthalic anhydride with aliphatic alcohols (linear/branched) with four to fifteen carbon atoms, epoxidized soyabean oil, esters of trimellitic acids, phosphates, esters of benzoic and citric acids, and halogenated hydrocarbons. Higher molecular weight polyesters (800-6000) prepared by condensation of diols with adipic or sebacic acids are also used as plasticizers. Of these, phtlhalate based plasticizers are the most widely used because of their excellent compatibility with PVC, ease of fusion and all round desirable properties.
Nevertheless, phthalate esters are not without drawbacks. Dioetylphthalate has been implicated as a carcinogen causing liver cancer in rats. Their molecular weights are low on account of which they diffuse out of PVC rapidly and cause xe2x80x9cfoggingxe2x80x9d (cloudy dsposits) of glasses and other transparent surfaces. They are easily extracted by organic solvents, making them unsuitable for use in solvent contact applications. They produce PVC products whose surface resistivity is very high (approximately 4xc3x971014 xcexa9 at 30xc2x0 C.) for many applications such as antistatic products for hospitals flooring materials, footwear, hoses, clean room fixtures, trays for integrated circuits and floppy discs, conveyor belt etc. The surface resistivity can be brought down by a factor of 101-102 by adding an antistat additive (example Irgastat 51 of Ciba Geigy). However, use of such additives leads to loss of desirable properties of PVC. The thermal and light stability is adversely affected and the antistatic additive exudes out of PVC.
To overcome the above problems envisaged in the prior art, the applicants have now provided a novel compound bearing an urethane. linkage shown in formula 1 of the drawings, which is useful as a plasticizer for PVC; a process for preparing such compound and, a manner in which a compounded PVC is prepared by employing the novel compound.
Therefore, one object of the present invention is to provide a compound having an urethane linkage of formula 1 of the drawings.
Another object of the invention relates to a process for the preparation of new plasticizer for PVC.
Yet another object of the present invention is to provide a process for the preparation of new plasticizer derived from fatty acid esters and a hydroxyl group, and an isocyanate bearing organic compound.
Still another object of the present invention is to provide a process for the preparation of improved compounded polyvinyl chloride using the compound of formula 1 of the enclosed drawings as a primary plasticizer. The use of compound of formula 1 in conjunction with PVC confers on PVC many desirable properties such as flexibility, softness, good mechanical and thermal properties. In addition, use of compound of formula 1 eliminates many of the drawbacks of the hitherto known plasticizers for PVC.
Further object of the invention is for a compounded PVC comprising polyvinyl chloride and a plasticizer of formula 1 of the drawings enclosed with the specification wherein Ar is as defmed in the said drawings.
In the course of the applicants research, they have developed a process for the preparation of a new organic compound of the formula 1 of the drawings wherein Aryl (Ar) is as defined in the annexed drawings which show useful properties as primary plasticizer for PVC. The compound of formula 1 is derived from the reaction of fatty acid esters having eighteen carbon atoms and a hydroxyl group, and organic isocyanates.
The fatty acid esters suitable for die present invention are esters of ricinoleic acid and 12 hydroxyl stearic acid. The ester can be derived by reacting ricinoleic acid or 12 hydroxystearic acid with an alcohol having a linear or branched alky group having 1-10 carbon atoms.
The isocyanate useful in the process of the present invention can be selected from any organic isocyanates having one or two isocyanate groups per molecule. Examples are toluene diisocyanate of formula 3 as shown in the drawings, 4,4xe2x80x2-diisocyanatodipheniylmetlhane of formula 4 as shown in the drawings, 1,4-diisocyanatobenzene of formula 5 as shown in the drawings, hexamethylene diisocyaniate of formula 6 as shown in the drawings, isophorone diisocyanate of formula 8 as shown in the drawings, 1,4-diisocyanatocyclohexane of formula 7 as shown in the drawings. The preferred isocyanates are those derived from aromatic compounds and having at least two isocyanate groups.
Accordingly, the present invention provides a novel compound bearing urethane linkage having formula 1 of the drawings accompanying this specification.
The invention also provides a process for the preparation of a compound bearing urethane linkage having fonnula 1 shown in the drawings accompanying the specification useful as a plasticizer for PVC which comprises reacting fatty acid esters bearing hydroxyl groups with an organic isocynate at a temperature in the range of 30-100xc2x0 C. in the presence of a catalyst. The molar ratio of hydroxyl bearing fatty acid to the isocyanate may be in the range of 2:1.1, the preferred ration being 2:1.05. The catalyst employed in the reaction may be selected from any one of the following: di-n-butyltindilaurate, di-n-butyl-tinoxide, 1,4-diazabicyclo [2.2.2] octane (DABCO), 4xe2x80x2,4xe2x80x2-dimetlhylainino pyridine (DMAP) and 1,8-diazabicyclo [5.3.0] undec-7-ene (DBU). The concentration of the catalyst may range from 0.02-0.2% by weight of the isocyanate compound. The preferred concentration is in the range of 0.05%. The reaction is conducted for a period of 1-3 hours. The progress of the reaction is monitored by Brookfield viscosity and determination of lhydroxyl number. The final product should have a viscosity below 2500 centipoises at 27xc2x0 C. and have a hydroxyl number below 20 (expressed as mg KOH/g). The product molecular weight as measured by vapour pressure osmometry is in the range of 650-900 depending on the nature of the isocyanate.
The process of preparing the plasticizer is clean, does not produce any effluents or byproducts and is ready for use at the end of the reaction directly without any further processing.
The structures of the compounds prepared by the process of the present invention have been established by a variety of spectroscopic techniques such as infra red, nuclear magnetic resonance and mass spectrum. More specifically, a product derived from the reaction of ricinoleic acid methyl ester with toluene diisocyanate shows in infra red spectrum absorption at 3320, 1730-1750, and 1400-1600 inverse centimeters due to xe2x80x94NH, carbonyl and xe2x80x94HCxe2x95x90CHxe2x80x94 groups. The nuclear magnetic resonance shows peaks at 0.9-2.5, 3.6-3.7, 5.0-6.0 and 6.5-7.5 ppm corresponding to the methyl groups, methoxy group, vinylic hydrogen and aromatic hydrogen attached to ring.
The invention further provides a process for the preparation of a compounded PVC, which process comprises mixing a compound of formula 1 shown in the drawing accompanying this specification at a temperature in the range of 120xc2x0 to 150xc2x0 C. and in the presence of a stabiliser and if desired, preparing the sheets of the compounded PVC, so prepared, of the desired dimensions by conventional methods.
The advantages of using the compound of the formula 1 are:
1. The compound is compatible with both PVC and phthalate type plasticizers, enabling its use either by itself as a primary plasticizers or in blends with phthalates, if necessary.
2. It has a high molecular weight and thus low tendency to migrate or exude from the surface.
3. It is derived from naturally occurring fatty acids and possess urethane type linkages, which has been established in the prior art as biocompatible (Ref: Japan Patent 7650,958 dated May 6, 1976 to Dainippon Ink and Chemicals Inc.). Hence, the plasticizer should show very low toxicity.
4. Its polar character makes it poorly soluble in organic solvents. Hence PVC plasticized by compounds of formula 1 show excellent resistance to extraction by organic solvents.
5. PVC plasticized by plasticizers of formula 1 show exceptionally low surface resistivities (6xc3x97109 xcexa9 30xc2x0 C.) without addition of any antistatic additives.
The plasticizer, prepared by the process as described above is compounded with PVC in an electrically heated two roll mill in presence of stabilizers to form a smooth sheet of 150 mmxc3x97150 mmxc3x972 mm size. The content of plasticizer used may be in the range of 40 to 60 parts per hundred parts of the resin (phr). The preferred composition is 50 phr. The urethane plasticizer can also be incorporated in blends with ester type plasticizers well known in the prior art. For example, urethane plasticizer can be blended with di-2-ethylhexylphthalate (DOP) in an amnount ranging from 10:90 to 90:10 proportions prior to incorporation in PVC. The stabilizers added are chosen from a variety of metal stearates well known in prior art. The metal stearates can be derived from barium, cadmium, calcium, zinc and the like. The concentration of the stabilizers is in the range of 1-5 phr, preferred concentration being 3 phr. The dry blend of PVC, plasticizer and the stabilizers are mixed in a two roll mill at the temperature range 120-150xc2x0 C. for 2-10 minutes, till complete and uniform fusion of the blend occurs. The sheet is then used for preparing test specimens which are tested for properties as per methods prescribed by American Society of Testing Materials (ASTM). The results are shown in Table 1 where the performance of the urethane plasticizer is compared with di-2-etlhylhexylphthalate (DOP) under identical conditions (Table 1). The mechanical as well as high and low temperature properties of urethane and DOP plasticizers are essentially similar. However, dramatic improvements are observed with regard to extractability in organic solvents and surface resistivity. The results confirm that the compound of formula 1, is a primary plasticizer for PVC and possesses useful properties which are not present in DOP type plasticizers.
b. Compound of formula 1 prepared by the reaction of ricinoleic acid with toluenediisocynate.
c. Di-2-ethylhexylphthalate